Certain (R)-3,4-dihydro-4-alkylamino-2-substituted-2H-thieno[3,2-e]-1,2-thiazine-6 -sulfonamide-1,1-dioxides of the structural formula I (shown below) have previously been prepared by resolution of the racemate via the di-p-toluoyl-D-tartaric acid salt or from (S)-3,4-dihydro-4-hydroxy-2-substituted-2H-thieno[3,2-e]-1,2-thiazine-6-su lfonamide-1,1-dioxides by activation of the C(4)-hydroxyl group and displacement with the appropriate amine. Both of these methods, as well as a process for the preparation of the requisite (S)-3,4-dihydro-4-hydroxy-2-substituted-2H-thieno[3,2-e]-1,2-thiazine-6-su lfonamide-1,1-dioxides from 3-acetylthiophene, are disclosed by Dean et al. in PCT/U.S. Ser. No. 91/02262. The present invention provides an improved process for the preparation of (R)-3,4-dihydro-4-alkylamino-2-substituted-2H-thieno[3,2-e]-1,2-thiazine-6 -sulfonamide-1,1-dioxides from 3-acetyl-2,5-dichlorothiophene.